The synthesis of new inorganic and organic substances, the question of their reaction and degradation products and the interest in the possible occurrence of trace-like impurities during the synthesis and/or reaction and/or degradation of these substances always impose new and increasingly stringent demands upon detection analysis. This applies in particular to products in the pharmaceutical, plant protection and dyestuff fields. At the same, the need to simplify and automate these detection techniques also arises. This applies in particular to the clinical sector, to medicaments and also to the analysis of harmful substances in insecticides, herbicides and fungicides and of environmentally polluting substances in effluents and waste gases. There is also interest in processes which can assist in the qualitative and quantitative detection of trace-like substances present in various concentrations in a wide range of other components, the nature of the substances to be detected or the associated group of substances being known per se. Problems of this nature frequently arise, for example, in clinical diagnosis or in the main laboratories of large chemical works.
To this end, high-quality separation and detection techniques have been and are being developed. Particular mention is made here of separation processes based on high-pressure liquid chromatography (HPLC) and thin-layer chromatography (TLC) and, generally in offline combination with such separating methods, mass spectrometers. In their case, the separate moelcules are ionized by field desorption, by laser-stimulated ion desorption, by the californium technique, by chemical ionization and by ion activation (secondary ion mass spectrometry). A survey of the present state of the art was presented, for example, at the 1981 Pittsburgh Conference.
In addition, the known method of paper strip chromatography has already been combined with a mass spectrometer. Preliminary separation of the mixture of substances takes place in the strip of paper. The strip of paper is then introduced into a mass spectrometer and the patches associated with the individual substances are analyzed by SIMS (cf. R.J. Day et al, Anal. Chem. 52, No. 4 (1980), pages 557a-572a). One of the disadvantages of these methods lies in the fact that the preliminary separation step takes place chromatographically and requires long analysis times. In many cases, the preliminary separation step is made difficult or even impossible, above all when the individual components differ only slightly from one another in regard to their rate of migration. One feature common to all chromatographic separation techniques is that they are based on a volume effect, in other words, the separation effect is based on transport phenomena taking place in a porous support layer several thousand molecule layers thick. In addition, relatively large quantities of substances have to be used on account of the large inner surface of the substrate.
Preliminary separation by means of a porous sintered element in combination with mass spectrometric detection is described in British Patent Specification No. 2,008,434. However, the process in question is confined to substances which can evaporate from the sintered element in the mass spectrometer. This is because the enriched substance in the sintered element is converted by heating into the gas phase and then ionized, for example by electron bombardment or by field ionization. Direct ionisation on the solid is not possible. Preliminary separation is based either on a chromatographic separation effect or is attributable to a form of fractional distillation within the sintered element. The main disadvantage of this process lies in the fact that thermally labile substances can undergo complete or partial decomposition during their thermal elimination from the sintered element with the result that defective or non-evaluatable mass spectra are obtained. This applies in particular to organic compounds of high molecular weight.